Inverse Compton Emission from Galactic Supernova Remnants: Effect of the Interstellar Radiation Field

By Troy A. Porter, Igor V. Moskalenko, A. Strong. 2006

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The evidence for particle acceleration in supernova shells comes from electrons whose synchrotron emission is observed in radio and X-rays. Recent observations by the HESS instrument reveal that supernova remnants also emit TeV γ-rays, long-awaited experimental evidence that supernova remnants can accelerate cosmic rays up to the "knee" energies. Still, uncertainty exists whether these γ-rays are produced by electrons via inverse Compton scattering or by protons via π0-decay. The multiwavelength spectra of supernova remnants can be fitted with both mechanisms, although a preference is often given to π0-decay due to the spectral shape at very high energies. A recent study of the interstellar radiation field indicates that its energy density, especially in the inner Galaxy, is higher than previously thought. In this Letter we evaluate the effect of the interstellar radiation field on the inverse Compton emission of electrons accelerated in a supernova remnant located at different distances from the Galactic center. We show that contribution of optical and infrared photons to the inverse Compton emission may exceed the contribution of cosmic microwave background and in some cases broaden the resulting γ-ray spectrum. In addition, we show that if a supernova remnant is located close to the Galactic center, its γ-ray spectrum will exhibit a "universal" cutoff at very high energies due to the Klein-Nishina effect and not due to the cutoff of the electron spectrum. As an example, we apply our calculations to the supernova remnants RX J1713.7-3946 and G0.9+0.1, recently observed by HESS.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/fe0c65c4b82aa7f84b2aee8c5bc40a212b122c14

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Citations in the corpus

THE LARGE AREA TELESCOPE ON THE FERMI GAMMA-RAY SPACE TELESCOPE MISSION (2009, background): “9+0.1, LAT observations will probe the inverse Compton emission mechanism and the interstellar radiation field at the Galactic center (Porter et al. 2006).”
OBSERVATIONS OF THE YOUNG SUPERNOVA REMNANT RX J1713.7−3946 WITH THE FERMI LARGE AREA TELESCOPE (2011, background): “The main argument75 revolves around two main emission mechanisms (Aharonian et al. 2006; Katz & Waxman76 2008; Berezhko & Völk 2008; Porter et al. 2006; Ellison & Vladimirov 2008; Morlino et al.77 2009), but so far, conclusive evidence for either possibility is still missing.”
Galactic Center gamma-ray ``excess'' from an active past of the Galactic Centre? (2014, methodology): “For the spectral density of the ISRF field nISRF we took the values which correspond to the ones used in the GALPROP code3, for the inner Galaxy, as shown in [21].”
Study of Nonthermal Emission from SNR RX J1713.7–3946 with Suzaku (2008, methodology): “For calculations of IC fluxes we used the diffuse photon fields proposed by Porter et al. (2006), including 2.7 K CMB, as well as interstellar radiation consisting of two, optical (starlight) and infrared (dust) emission components.”
Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge (2008, methodology): “We briefly describe our calculation of the ISRF; further details can be found in Moskalenko et al. (2006) and Porter et al. (2006).”